Points 1. Following is the overall reaction catalyzed by the Calvin-Benson cycle:

Transcription

1 BCH 4054 February 22, 2002 HOUR TEST 2 NAME_ Points 1. Following is the overall reaction catalyzed by the Calvin-Benson cycle: CO 2 + 3ATP + 2NADPH 1/3 glyceraldehyde-3-p + 3ADP + 2NADP + Give the structures of reactants and products for the step or steps of the cycle which: Page Points (4) (a) Incorporates CO 2 into an organic form (one reaction). Total (8) (b) Use ATP as a substrate (two reactions). (4) (c) Uses NADPH as a substrate (one reaction). (6) 2. An alternative fixation of CO 2 into organic form occurs in tropical grasses which are called C-4 plants. This alternative C-4 pathway is called the Hatch-Slack pathway. Give the structures of the reactants and products for this reaction of CO 2, and explain what function this pathway serves.

2 BCH Hour Test 2 Page 2 Name 3. Pyruvate kinase has a very large negative G o ', and so the reaction operates with a large negative G and is essentially irreversible. (8) (a) How do animal cells carry out the conversion of pyruvate to phosphoenol pyruvate? Give the reactants, products, (names or structures) and the name(s) of the enzyme(s) involved. (4) (b) How do C-4 plant cells carry out this conversion? Give the reactants, products, (names or structures) and the name(s) of the enzyme(s) involved. (10) 4. One of the key reactions of both the Calvin-Benson cycle and the phosphgluconate pathway is catalyzed by the enzyme transketolase. (a) Give the structure and name of the products formed when this enzyme catalyzes the reaction between fructose-6-phosphate and glyceraldehyde-3-phosphate. (b) What prosthetic group is found on transketolase?

3 BCH Hour Test 2 Page 3 Name (10) 5. Stimulation of liver by the hormone glucagon results in several metabolic changes that lead to the increase in glucose synthesis and excretion by liver. One of these changes involves inhibition of glycolysis and stimulation of gluconeogenesis (i.e. the conversion of phosphoenolpyruvate to glucose). Describe all the steps and intermediates involved in this stimulation, beginning with the hormone interacting with its cellular receptor, and ending with the glycolytic/gluconeogenic enzymes that are affected. (6) 6. Metabolic compartmentation plays an important role in metabolic regulation because not all intermediates can cross intracellular membranes. For example, fatty acids are activated in the cytoplasm to the CoASH esters, but must enter the mitochondrial matrix in order for oxidation to occur. Explain how fatty acyl-coa esters are transported across the inner mitochondrial membrane.

4 BCH Hour Test 2 Page 4 Name 7. As a way of comparing the energy available from the oxidation of fatty acids to that available from the oxidation of carbohydrates, one could compare the ATP produced from the oxidation of a six carbon fatty acid (hexanoic acid: CH 3 CH 2 CH 2 CH 2 CH 2 COOH) with that produced from a six carbon sugar (glucose). Following is a summary of the ATP calculation for glucose, assuming 2.5 ATP per mitochondrial NADH and 1.5 ATP per cytoplasmic NADH and mitochondrial CoQH 2. hexokinase and PFK-1-2 ATP glyceraldehyde-3-p 2 cytoplasmic NADH 2 x 1.5 = 3 ATP dehydrogenase 3-phosphoglycerokinase 2 ATP pyruvate kinase 2 ATP Pyruvate dehydrogenase 2 mitochondrial NADH 2 x 2.5 = 5 ATP 2 acetyl-coa 3 x 2 NADH 6 x 2.5 = 15 ATP in TCA cycle 2 CoQH 2 2 x 1.5 = 3 ATP 2 GTP equiv. to: 2 ATP Total net per glucose: 30 ATP (14) (a) Sketch the pathway, including structures of all intermediates derived from hexanoic acid, for the degradation of hexanoic acid to acetyl-coa in the mitochondrial matrix, showing utilization or production of coenzyme cosubstrates ATP, GTP, CoQH 2 and NADH. Assume that hexanoic acid is activated in the mitochondrial matrix in the same way as acetoacetate, not in the cytoplasm as longer chain fatty acids are activated. (6) (b) Summarize the overall ATP production for complete oxidation of hexanoic acid in a manner similar to that done for glucose above. There is no need to give the detailed steps for breakdown of acetyl-coa by the TCA cycle, but show the calculation of ATP s for that process.

5 BCH Hour Test 2 Page 5 Name For questions 8-17, check the blank corresponding to the best answer. (2 pts each question) 8. Which of the following is not a ketone body: acetoacetate betahydroxy butyrate oxaloacetate acetone 9. Muscle is unable to synthesize glucose because it lacks the enzyme: phosphorylase hexokinase glucose-6-phosphatase F-1,6-BPase pyruvate kinase 10. The enzyme interconverting ribose-5- phosphate and ribulose-5-phosphate is: triose phosphate isomerase hexose phosphate isomerase pentose phosphate epimerase pentose phosphate kinase pentose phosphate carboxylase 11. The enzyme interconverting xylulose-5- phosphate and ribulose-5-phosphate is: triose phosphate isomerase hexose phosphate isomerase pentose phosphate epimerase pentose phosphate kinase pentose phosphate carboxylase 12. Chylomicrons carry triglycerides made from which are hydrolyzed in the blood by the enzyme. dietary fat; pancreatic lipase adipose tissue fat, lipoprotein lipase biosynthetic fat, hormone sensitive lipase dietary fat, lipoprotein lipase adipose tissue fat, hormone sensitive lipase biosynthetic fat, pancreatic lipase 13. Which enzyme is found in the phosphogluconate pathway, but not in the Calvin-Benson cycle? transketolase aldolase transaldolase ribulose bis phosphate carboxylase 14. Which enzyme does not produce NADPH as a product? malate dehydrogenase malic enzyme glucose-6-phosphate dehydrogenase 6-phosphogluconate dehydrogenase 15. Liver cannot degrade acetoacetate because it lacks the enzyme thiolase carnitine acyl transacylase beta-ketoacyl CoA transferase thiokinase citrate synthase 16. Odd chain fatty acids are degraded to propionyl-coa. The first step in its degradation is conversion to by the enzyme _. succinyl-coa; methylmalonyl-coa mutase methylmalonyl-coa; propionyl-coa carboxlase hydroxymethylglutaryl-coa; HMG- CoA synthase acetyl-coa; propionyl-coa decarboxylase 17. In the Cori cycle, circulates from the liver to the muscle, and _ circulates from the muscle to the liver. acetoacetate; lactate lactate; glucose pyruvate, glucose glucose, acetoacetate glucose, lactate glucose, pyruvate